A known variable valve timing control device is disclosed in Japanese Patent Laid-Open Publication No. 2002-295208. This variable valve timing control device includes a shoe housing (rotation transmitting member) rotatable with one of a driving shaft and a driven shaft, and a vane rotor rotatable with the other one of the driving shaft and the driven shaft and having a vane that divides a concave portion formed in the shoe housing into an advanced angle chamber and a retarded angle chamber. The variable valve timing control device also includes a torsion coil spring whose one end engages with the shoe housing or a member rotatable as a unit with the shoe housing and whose other end engages with the vane rotor for biasing the vane rotor to an advanced angle side or a retarded angle side relative to the shoe housing. An end portion of the torsion coil spring engaging with the vane rotor is provided, being perpendicular to the axial direction of the van rotor. The vane rotor includes a hook groove formed in a direction perpendicular to the axial direction of the vane rotor and with which the end portion of the torsion coil spring engages.
According to the disclosed variable valve timing control device, a gap is formed around substantially entire outer circumference of the end portion of the torsion coil spring when the end portion of the torsion coil spring engages with the hook groove of the rotor. Therefore, the vibration of an internal combustion engine and a chain system, the pulsation of the fluid pressure, the friction of cams and a resultant force thereof cause the torsion coil spring to vibrate in the axial direction, the vertical direction and the rotational direction via the gap whereby the resonance is generated torsion coil spring under a predetermined frequency. Due to this resonance, an appropriate torque for biasing the vane rotor on the advanced angle side or the retarded angle side cannot be assured by the torsion coil spring and thus a poor performance of the variable valve timing may be caused. In addition, a problem such as the abrasion development in each contact portion of each member and a fatigue fracture of the torsion coil spring itself may be raised. Thus, a need exists for a variable valve timing control device that can prevent the vibration of the torsion coil spring.